Resistance welding (also known as electric-resistance welding) is a known metallurgical process used to weld a right-angle end flange of a tube to a surface projection of a plate wherein metal is heated by its own resistance to a semi-fused (i.e., soft) or fused (i.e., molten) state by the passage of very heavy electric currents for very short lengths of time and then welded. In one known variation, the plate is stamped creating depressions on the top surface and creating surface projections on the bottom surface so that during the resistance welding, the projections soften and/or melt creating a weld nugget which joins together the plate to the tube flange.
Conventional methods for welding a tube to another tube or for welding a tube to a plate include gas metal arc welding. Gas metal arc welding uses a consumable metal wire as one electrode and the parts as another electrode, and moves the consumable metal wire (or the parts) to draw an arc and weld the parts together. The welding is accompanied by a gas (such as a mixture of argon and carbon dioxide) to prevent oxidation and stabilize the arc. Such gas metal arc welding is well known. In a conventional gas metal arc welding technique, solid metal wire or metal core wire (i.e., an annular-solid wire whose core is filled with metal powder such as a mixture of metal, alloy and/or oxide powders) is used with the wire usually at a positive electrical welding potential and with the parts electrically grounded. The welding arc creates a molten weld puddle which results in the welding together of the parts. A ceramic ferrule is used to contain the weld puddle when needed. Gas metal arc welding requires expensive welding equipment, the molten weld puddle tends to flow away from the joint area (depending on the joint position with respect to gravity) resulting in welds of inconsistent quality, and the process requires a long cycle time between welds.
Conventional methods for attaching parts together also include friction welding. To join two tubes together end to end, one of the tubes is rotated about its longitudinal axis, and the tube ends are pressed together, wherein friction causes heating of the ends creating the weld. To join a tube to a plate, the tube is rotated about its longitudinal axis, and the tube end and the plate are pressed together, wherein friction causes heating creating the weld. Friction welding requires expensive welding equipment, and the process requires a long cycle time between welds. Friction welding is not easily applicable to thin-walled tubes because they do not retain their shapes well under heat and pressure. It is noted that laser and electron-beam welding for the above joints also need expensive equipment and expensive joint preparation.
Conventional brazing is a known metallurgical process used to join together two metal members. In this method, a brazing material is interposed between the two members, and external heat is applied to the assemblage which bonds the brazing material to the two members. Typically, a batch of assemblages of member pairs with interposed brazing material is heated in an oven or by an infrared heat source. In some applications, the members tend to become distorted from the oven or infrared heat. Conventional brazing requires expensive heating equipment and batch heat processing of the assemblages.
What is needed is a less expensive method for metallurgically joining a tube to a member.